Temperature-based monitoring method and system for determining first and second fluid flow rates through a heat exchanger

ABSTRACT

Monitoring method and system are provided for dynamically determining flow rate of a first fluid and a second fluid through a heat exchanger. The method includes: pre-characterizing the heat exchanger to generate pre-characterized correlation data correlating effectiveness of the heat exchanger to various flow rates of the first and second fluids through the heat exchanger; sensing inlet and outlet temperatures of the first and second fluids through the heat exchanger, when operational; automatically determining flow rates of the first and second fluids through the heat exchanger using the sensed inlet and outlet temperatures of the first and second fluids and the pre-characterized correlation data; and outputting the determined flow rates of the first and second fluids. The automatically determining employs the determined effectiveness of the heat exchanger in interpolating from the pre-characterized correlation data the flow rates of the first and second fluids.

TECHNICAL FIELD

The present invention relates in general to heat exchanger monitoringand management, and more particularly, to monitoring methods and systemsfor ascertaining fluid flow rates through a heat exchanger tofacilitate, for example, management of cooling within a facilitycontaining the heat exchanger, such as a data center containing one ormore heat exchangers facilitating cooling of electronic components withthe data center.

BACKGROUND OF THE INVENTION

The power dissipation of integrated circuit chips, and the modulescontaining the chips, continues to increase in order to achieveincreases in processor performance. This trend poses a cooling challengeat both the module and system level. Increased airflow rates are neededto effectively cool high power modules and to limit the temperature ofair that is exhausted into the computer center.

In many large server applications, processors along with theirassociated electronics (e.g., memory, disk drives, power supplies, etc.)are packaged in removable drawer configurations stacked within a rack orframe. In other cases, the electronics may be in fixed locations withinthe rack or frame. Typically, the components are cooled by air moving inparallel airflow paths, usually front-to-back, impelled by one or moreair moving devices (e.g., fans or blowers). In some cases it may bepossible to handle increased power dissipation within a single drawer byproviding greater airflow, through the use of a more powerful air movingdevice or by increasing the rotational speed (i.e., RPMs) of an existingair moving device. However, this approach is becoming problematic at therack level in the context of a computer installation (i.e., a datacenter).

The sensible heat load carried by the air exiting the rack is stressingthe ability of the room air-conditioning to effectively handle the load.This is especially true for large installations with “server farms” orlarge banks of electronics racks close together. In such installationsnot only will the room air-conditioning be challenged, but the situationmay also result in recirculation problems with some fraction of the“hot” air exiting one rack unit being drawn into the air inlet of thesame rack or a nearby rack. This recirculating flow is often extremelycomplex in nature, and can lead to significantly higher rack inlettemperatures than expected. This increase in cooling air temperature mayresult in components exceeding their allowable operating temperature andin a reduction in long term reliability of the components.

SUMMARY OF THE INVENTION

The shortcomings of the prior art are overcome and additional advantagesare provided in one aspect through the provision of a method ofmonitoring a heat exchanger. The method includes: pre-characterizing aheat exchanger to generate pre-characterized correlation data for theheat exchanger, the pre-characterized correlation data comprising datacorrelating effectiveness of the heat exchanger to flow rates of a firstfluid through the heat exchanger and flow rates of a second fluidthrough the heat exchanger, wherein when operational, heat istransferred across the heat exchanger between the first fluid and thesecond fluid; sensing inlet and outlet temperatures of the first fluidpassing through the heat exchanger when operational; sensing inlet andoutlet temperatures of the second fluid passing through the heatexchanger when operational; automatically determining at least one of aflow rate of the first fluid through the heat exchanger or a flow rateof the second fluid through the heat exchanger, the automaticallydetermining employing the pre-characterized correlation data and thesensed inlet and outlet temperatures of the first fluid and the sensedinlet and outlet temperatures of the second fluid; and outputting thedetermined flow rate of the first fluid or flow rate of the second fluidthrough the heat exchanger.

In another aspect, a monitoring system for a heat exchanger is provided.The monitoring system includes a database holding pre-characterizedcorrelation data for the heat exchanger. The pre-characterizedcorrelation data includes data correlating effectiveness of the heatexchanger to flow rates of a first fluid through the heat exchanger andflow rates of a second fluid through the heat exchanger, wherein whenoperational, heat is transferred across the heat exchanger between thefirst fluid and the second fluid. The monitoring system furtherincludes: a first inlet temperature sensor for sensing inlet temperatureof the first fluid passing through the heat exchanger when operational;a first outlet temperature sensor for sensing outlet temperature of thefirst fluid passing through the heat exchanger when operational; asecond inlet temperature sensor for sensing inlet temperature of thesecond fluid passing through the heat exchanger when operational; asecond outlet temperature sensor for sensing outlet temperature of thesecond fluid passing through the heat exchanger; and a monitor unitcoupled to the first and second inlet temperature sensors and the firstand second outlet temperature sensors for obtaining the sensed inlet andoutlet temperatures of the first and second fluids. The monitor unitemploys the sensed inlet and outlet temperatures of the first and secondfluids and the pre-characterized correlation data in automaticallydetermining at least one of flow rate of the first fluid through theheat exchanger or flow rate of the second fluid through the heatexchanger, and outputs the determined flow rate of the first fluid orthe flow rate of the second fluid through the heat exchanger.

In a further aspect, a data center is provided which includes a heatexchanger for facilitating cooling of at least one electronics rackwithin the data center; and a monitoring system for monitoring the heatexchanger. The monitoring system includes a database holdingpre-characterized correlation data for the heat exchanger. Thepre-characterized correlation data includes data correlatingeffectiveness of the heat exchanger to flow rates of a first fluidthrough the heat exchanger and flow rates of a second fluid through theheat exchanger, wherein when operational, heat is transferred across theheat exchanger between the first fluid and the second fluid. Themonitoring system further includes: a first inlet temperature sensor forsensing inlet temperature of the first fluid passing through the heatexchanger when operational; a first outlet temperature sensor forsensing outlet temperature of the first fluid passing through the heatexchanger when operational; a second inlet temperature sensor forsensing inlet temperature of the second fluid passing through the heatexchanger when operational; a second outlet temperature sensor forsensing outlet temperature of the second fluid passing through the heatexchanger when operational; and a monitor unit coupled to the first andsecond inlet temperature sensors and the first and second outlettemperature sensors for obtaining the sensed inlet and outlettemperatures of the first and second fluids. The monitor unit employsthe sensed inlet and outlet temperatures of the first and second fluidand the pre-characterized correlation data in automatically determiningat least one of flow rate of the first fluid through the heat exchangeror flow rate of the second fluid through the heat exchanger, and outputsthe determined flow rate of the first fluid or the flow of the secondfluid through the heat exchanger.

Further, additional features and advantages are realized through thetechniques of the present invention. Other embodiments and aspects ofthe invention are described in detail herein and are considered a partof the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1. depicts one embodiment of a data center room layout including aplurality of electronics racks, a plurality of computer roomair-conditioning units, and a coolant distribution unit, and containingmultiple heat exchangers to be monitored, in accordance with an aspectof the present invention;

FIG. 2 is a cross-sectional elevational view of one embodiment of acomputer room air-conditioning unit of the plurality of computer roomair-conditioning units depicted in FIG. 1, and illustrating oneembodiment of a monitoring system for the heat exchanger thereof, inaccordance with an aspect of the present invention;

FIG. 3 is a cross-sectional elevational view of one embodiment of anelectronics rack with a rear door heat exchanger and a monitoring systemfor the heat exchanger, in accordance with an aspect of the presentinvention;

FIG. 4 is a schematic of one embodiment of fluid flows through a heatexchanger within a modular cooling unit or within a coolant distributionunit to be monitored, in accordance with an aspect of the presentinvention;

FIG. 5 is a schematic of a generalized heat exchanger with fluid A andfluid B to be monitored, in accordance with an aspect of the presentinvention;

FIG. 6A is a graph of pre-characterized correlation data for a heatexchanger relating heat exchanger effectiveness to fluid A and fluid Bflow rates, wherein fluid A has a lower heat capacity rate than fluid B,in accordance with an aspect of the present invention;

FIG. 6B is a graph of pre-characterized correlation data relating heatexchanger effectiveness to fluid A and fluid B flow rates, wherein fluidB has a lower heat capacity rate than fluid A, in accordance with anaspect of the present invention;

FIGS. 7A-7D graphically illustrate one example of the use of thepre-characterized correlation data of FIG. 6A and a stepwise estimatingof the flow rates of fluid B and fluid A, and interpolating of actualflow rates for fluid B and fluid A, in accordance with an aspect of thepresent invention;

FIGS. 8A-8D graphically illustrate one example of the use of thepre-characterized correlation data of FIG. 6B, and a stepwise analyzingof the flow rates of fluid B and fluid A and interpolating of actualfluid B and fluid A flow rates, in accordance with an aspect of thepresent invention; and

FIGS. 9-13 are a flowchart of one embodiment of processing implementedby a monitoring unit to ascertain fluid A and fluid B flow rates fromonly pre-characterized correlation data (e.g., the data represented byFIGS. 6A & 6B) and sensed fluid A inlet and outlet temperatures andfluid B inlet and outlet temperatures, in accordance with an aspect ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the terms “electronics rack”, “rack-mounted electronicequipment”, and “rack unit” are used interchangeably, and unlessotherwise specified include any housing, frame, rack, compartment, bladeserver system, etc., having one or more heat generating components of acomputer system or electronics system, and may be, for example, a standalone computer processor having high, mid or low end processingcapability. In one embodiment, an electronics rack may comprise multipleelectronics subsystems, each having one or more heat generatingcomponents disposed therein requiring cooling. “Electronics subsystem”refers to any sub-housing, blade, book, drawer, node, compartment, etc.,having one or more heat generating electronic components disposedtherein. Each electronics subsystem of an electronics rack may bemovable or fixed relative to the electronics rack, with the electronicsdrawers of a multi-drawer rack unit and blades of a blade center systembeing two examples of subsystems of an electronics rack to be cooled.

As used herein, “heat exchanger” means any heat exchange mechanismcharacterized as described herein through which a first fluid and asecond fluid pass, and wherein heat transfer occurs between the firstfluid and the second fluid across the heat exchanger. An air-to-air heatexchanger, an air-to-liquid heat exchanger, and a liquid-to-liquid heatexchanger are examples of a heat exchanger, as employed herein. Further,the concepts described below are applicable to any first and secondfluid, referred to herein as fluid A and fluid B, which flow inparallel, or counter or across each other within the heat exchanger.Further, a heat exchanger may comprise one or more discrete heatexchange devices coupled in-series or in parallel, and may include oneor more fluid flow paths, formed of thermally conductive tubing (such ascopper or other tubing). Size, configuration and construction of theheat exchanger can vary without departing from the scope of theinvention disclosed below. In addition, “data center” refers to acomputer installation containing one or more electronics racks to becooled. As a specific example, a data center may include one or morerows of rack-mounted computing units, such as server units.

One example of fluid A is air and fluid B is a coolant, such as water.In another example, fluid A is a facility coolant and fluid B a systemcoolant, with water being one example of the facility coolant and thesystem coolant. However, the concepts disclosed herein are readilyadapted to use with other types of coolant. For example, one or more ofthe liquid coolants may comprise a brine, a fluorocarbon liquid, aliquid metal, or other similar coolant, or refrigerant, while stillmaintaining the advantages and unique features of the present invention.Unless otherwise specified, “fluid” refers to either a gas or a liquid,such as air or a gaseous coolant, or a liquid coolant.

Reference is made below to the drawings, which are not drawn to scale tofacilitate conceptual understanding, and wherein the same referencenumbers are used throughout different figures to designate the same orsimilar components.

FIG. 1 depicts one embodiment of a raised floor, data center room layout100 comprising a plurality of heat exchangers to be monitored, inaccordance with an aspect of the present invention. In this layout,multiple types of electronics racks, 110, 111 & 112 are disposed in tworows. A computer installation such as depicted in FIG. 1 may houseseveral hundred, or even several thousand, microprocessors. In thearrangement of FIG. 1, chilled air enters the computer room floor viaperforated tiles 160 from a supply air plenum 145 defined between theraised floor 140 and a base or sub-floor 165 of the room. Cooled air istaken in through louvered front covers 121 at air inlet sides of theelectronics racks 110, 111 & 112 and expelled through louvered backcovers 131 (at the air outlet sides) of the electronics racks. Eachelectronics rack 110, 111 & 112 may have one or more air-moving devices(e.g., fans or blowers) to provide forced inlet-to-outlet airflow tocool the electronics within the subsystem(s) of the rack. The supply airplenum 145 provides conditioned and cooled air to the cold air inletsides of the electronics racks via the perforated floor tiles 160disposed in one or more “cold” air aisles of the computer installation.The conditioned and cooled air is supplied to plenum 145 via multiplecomputer room air-conditioning units (CRAC units) 150, also disposedwithin the computer installation 100, which reject heat from the roomair to facility coolant flowing through air-to-liquid heat exchangerstherein via facility coolant supply lines 151 and facility coolantreturn lines 152. Room air is taken into each computer roomair-conditioning unit 150 near an upper portion thereof. This room aircomprises in part exhausted air from the “hot” air aisles of thecomputer installation, with at least one side defined, for example, bythe air outlet sides of an adjacent row of electronics racks 110, 111 or112.

In this example, electronics racks 110 are air-cooled only, electronicsracks 111 are air-cooled and include, for example, a rear doorair-to-liquid heat exchanger (RDHx) for cooling air egressing from theelectronics rack, and electronics racks 112 are air-cooled electronicsracks employing liquid cooling of selected electronics components. Theliquid cooling is provided by, for example, one or more modular coolingunits (MCUs) disposed in the bottom of the rack. Coolant distributionunit 170 provides conditioned system coolant to electronics racks 111and includes, in one example, a liquid-to-liquid heat exchanger acrosswhich heat is rejected from the system coolant to facility coolantflowing through coolant distribution unit 170 via facility coolantsupply line 171 and facility coolant return line 172.

Air-cooled electronics racks 110 require proper functioning of computerroom air-conditioning units 150 to sustain reliable operation. If theCRAC units fail to supply sufficient quantities of cool air into thepressurized under-floor plenum, then the air-cooled components of theseelectronics racks may experience higher than specified devicetemperatures, thus leading to reduced reliability and possible failure.

The air and liquid-cooled electronics racks 111, with the rear door heatexchangers mounted to the rack require chilled and conditioned coolantfrom the coolant distribution unit to be able to remove a significantfraction of the heat load. One rear door heat exchanger (RDHx)embodiment for electronics rack 111 is described in co-pending, commonlyassigned U.S. patent application Ser. No. 11/108,306, entitled “Methodand Apparatus for Facilitating Cooling of an Electronics Rack Employinga Heat Exchange Assembly Mounted to an Outlet Door Cover of theElectronics Rack”, published Oct. 19, 2006 as U.S. Patent PublicationNo. 2006/0232945 A1.

Employing the rear door heat exchanger, a portion of the heat loadexhausting from electronics rack 111 is rejected to the coolant passingthrough the heat exchanger. This process reduces the cooling burden onthe room air-conditioning units when operational. If a problem arises,too much of the electronics rack heat load may be rejected into the roomambient air, resulting in a higher than anticipated burden on the CRACunits. This scenario may result in the room air temperature at theinlets to the nearby electronics racks rising as a result, which maylead to higher than anticipated device temperatures, thus compromisingsystem reliability.

Modular cooling units (MCUs) are located at the bottom of a hybridelectronics rack 112. These racks contain both air and liquid-cooledcomponents. The MCU(s) provides conditioned and cooled coolant tovarious liquid-cooled, high performance components located withinelectronics rack 112. One example of an electronics rack employing aMCU(s) is described in commonly assigned U.S. Pat. No. 7,011,143. If theMCU fails to function properly, and supplies warmer coolant or coolantat a lower flow rate than specified, then the high performanceliquid-cooled components within the electronics rack may quickly becomeoverheated and fail.

Thus, a common thermal element in the electronics racks depicted in FIG.1 is the need for proper functioning of the various heat exchangerslocated within the data center. Specifically, the heat exchangers withinthe CRAC units 150, the heat exchanger within the coolant distributionunit 170, the rear door heat exchangers of electronics racks 111, andthe heat exchangers of the MCUs of electronics racks 112 need tofunction properly. Three out of four of these heat exchange devices(i.e., the heat exchangers within the CRAC, CDU and MCU) are cooled attheir heat rejection side by chilled coolant, such as water, from afacility chiller refrigeration plant. To function properly within designmode, each of these heat exchangers requires the correct temperature ofchilled coolant and correct chilled coolant flow rate from the chillerplant. Each of the three device types (i.e., CRAC, CDU & MCU) has afluid-moving subassembly (for example, fan, blower or pump) that needsto supply the coolant at the correct volumetric flow rate. Thus, twocritical operating parameters common to three of the four heat exchangebased devices (CRAC, CDU & MCU) are the coolant flow rates on the systemside and the facility side, respectively. Depending on the device, thesystem side is the coolant loop (air or liquid) that directly cools theelectronic components, or the rear door heat exchanger. The facilityside is the chilled coolant loop from and returning to the chillerplant.

Described hereinbelow are a method and system for enabling thedetermination of fluid flow rates on each side of a fluid-to-fluid heatexchanger, such as the heat exchangers employed in the CRAC units, CDUunit, MCU units and RDHxs of FIG. 1, using only a pre-characterizationof the heat exchanger and dynamic fluid temperature measurements.

FIG. 2 illustrates one embodiment of a computer room air-conditioningunit 150 with a top to bottom airflow design, and which is used toprovide temperature-conditioned air for electronics rack cooling in araised floor data center configuration. As illustrated, warm computerroom air 200 enters CRAC unit 150 via an open vent 155 at an air inletof the CRAC unit, and flows through a set of air filters 210. Afterpassing through air filters 210, the filtered, warm air 220 is cooled asit passes across an air-to-liquid heat exchanger 230. Coolant isprovided via facility coolant supply line 151 and facility coolantreturn line 152. The filtered, warm air 220 is drawn acrossair-to-liquid heat exchanger 230 via one or more air-moving devices 240(e.g., fans or blowers) disposed in the lower portion of CRAC unit 150.Cooled air 250 is pushed by air-moving devices 240 into space 145 underthe raised floor to create the pressurized plenum needed to facilitateraised floor data center cooling via the perforated tiles discussedabove with reference to FIG. 1. The air-to-liquid heat exchanger istypically supplied with sub-ambient chilled coolant from a refrigerationchiller plant. This chilled coolant absorbs heat from the warm airpassing across the air-to-liquid heat exchanger, and rejects the heat tothe refrigeration chiller plant (not shown).

In the illustrated embodiment, a monitoring system is provided formonitoring fluid flow rates on each side of the air-to-liquid heatexchanger 230. This system includes one or more temperature sensors 260disposed at the air inlet side of air-to-liquid heat exchanger 230, andone or more temperature sensors 270 disposed at the air outlet side ofair-to-liquid heat exchanger 230. Data lines 285 couple thesetemperature sensors to a monitor unit 280, which in the embodimentillustrated, is attached to CRAC unit 150. Temperature sensors 260, 270are provided for monitoring (and allowing for respective averaging of,if desired) the air inlet temperature and air outlet temperature acrossair-to-liquid heat exchanger 230. Additionally, temperature sensors 290,291 are provided in fluid communication with facility coolant inlet line151 and facility coolant return line 152, respectively. Thesetemperature sensors 290, 291 monitor the inlet and outlet temperatures,respectively, of the liquid coolant flowing through air-to-liquid heatexchanger 230. Temperature sensors 290, 291 also provide temperaturedata via respective data lines 285 to monitor unit 280.

FIG. 3 is a side elevational view of one embodiment of an electronicsrack 111 employing a rear door heat exchanger (RDHx) 300. Electronicsrack 111 includes an air inlet side 120 and an air outlet side 130, withrespective louvered covers 121, 131 to facilitate airflow from the airinlet side to the air outlet side of the electronics rack. Electronicsrack 111 also includes a plurality of horizontally-disposed electronicssubsystems 115, such as a plurality of server nodes. As air flowsthrough the electronics rack, it passes over electronics subsystems 115,removing heat from the nodes and expelling the heat out air outlet side130 of the electronics rack.

Disposed in outlet door 131 is RDHx 300, which is an air-to-liquid heatexchanger, across which the inlet-to-outlet airflow through theelectronics rack passes. Coolant distribution unit 170 (FIG. 1) providesconditioned and cooled system coolant to rear door heat exchanger 300via system coolant supply line 301 and system coolant return line 302.Heat exchanger 300 removes heat from the exhausted inlet-to-outletairflow through the electronics rack via the system coolant, forultimate transfer in coolant distribution unit 170 (FIG. 1) to facilitycoolant passing therethrough via a liquid-to-liquid heat exchangerdisposed therein (described below). The RDHx cooling apparatusadvantageously reduces heat load on existing air-conditioning unitswithin the data center, and facilitates cooling of the electronics rackby cooling the air egressing from the electronics rack, thus cooling anyair recirculating to the air inlet side thereof.

In accordance with an aspect of the present invention, a monitoringsystem is provided which includes, in this embodiment, a plurality oftemperature sensors 310 disposed on the air inlet side of rear door heatexchanger 300 and a plurality of temperature sensors 320 disposed on theair outlet side of rear door heat exchanger 300, which are respectivelycoupled via data cables 315 to a monitor unit 320. Additionally, atemperature sensor 330 is disposed in fluid communication with systemcoolant supply line 301 to sense system coolant inlet temperature to theheat exchanger and a temperature sensor 331 is disposed in fluidcommunication with system coolant return line 302 to sense systemcoolant outlet temperature from the heat exchanger. These temperaturesensors 330, 331 are also coupled to monitor unit 320 via data cables315 for forwarding sensed temperature values to the monitor unit. In oneembodiment, monitor unit 320 is attached to electronics rack 111 in alocation which can be readily viewed by a site engineer in order toobtain flow rate results, as described further below.

FIG. 4 is a schematic of another embodiment of a monitoring system, inaccordance with an aspect of the present invention, applied to aliquid-to-liquid heat exchanger 410, which may be part of a modularcooling unit (MCU) or a coolant distribution unit 400. By way ofexample, the modular cooling unit may be disposed in a lower portion ofan electronics rack 112 (see FIG. 1), while the coolant distributionunit may be a freestanding unit within the data center, such as coolantdistribution unit 170 in data center 100 of FIG. 1. The modular coolingunit or coolant distribution unit 400 is associated with an electronicsrack 401, such as electronics rack 111 or electronics rack 112 inFIG. 1. Electronics rack 401 includes a heat transfer device 420, forexample, for extracting heat from air egressing from the air outlet sideof the heat exchanger in the electronics rack 111 embodiment discussedabove, or for extracting heat via conductive transfer from anelectronics module (not shown).

The heat extracted via heat transfer device 420 is transferred viasystem coolant (circulated via pump 425 through system coolant returnline 421 and system coolant supply line 422) to liquid-to-liquid heatexchanger 410 of the MCU or CDU 400. The system coolant loop and modularcooling unit (or coolant distribution unit) are designed to providecoolant of a controlled temperature and pressure, as well as acontrolled chemistry and cleanliness to the heat transfer device 420.The system coolant is physically separate from the less controlledfacility coolant in the facility coolant supply and return lines 171,172, respectively, to which heat is ultimately transferred.

In this embodiment, the monitoring system includes an inlet temperaturesensor 440 in fluid communication with the facility coolant supply line171 and an outlet temperature sensor 441 in fluid communication with thefacility coolant return line 172. Additionally, an inlet temperaturesensor 450 is in fluid communication with the system coolant return line421 and an outlet temperature sensor 451 is in fluid communication withthe system coolant supply line 422. Temperature sensors 440, 441, 450 &451 provide sensed temperature values to a monitor unit 460 viaappropriate data lines 455. Monitor unit 460 may be coupled to thecoolant distribution unit, or coupled to the electronics rack (dependingon the implementation) for ready access by a data center administratoror site engineer.

FIG. 5 is a schematic of a generic fluid A to fluid B heat exchanger500, wherein either fluid A or fluid B (or both fluid A and fluid B) maybe a gas or liquid. Heat exchanger 500 facilitates the exchange of heatbetween fluid A in fluid A loop 510 and fluid B in fluid B loop 520. Asshown, in accordance with an aspect of the present invention, an inlettemperature sensor 511 and outlet temperature sensor 512 are disposed influid A loop 510 for sensing inlet temperature T_(A1) and outlettemperature T_(A2), respectively, of fluid A. Similarly, an inlettemperature sensor 521 and outlet temperature sensor 522 are disposed influid communication with fluid B flowing through fluid B loop 520 tosense inlet temperature T_(B1) and outlet temperature T_(B2) of fluid B,respectively.

The monitoring method of the present invention is described below withreference to the generalized heat exchanger schematic of FIG. 5. Thisgeneric heat exchanger represents operation of the monitoring method andsystem disclosed herein for all of the various heat exchangerembodiments noted above in connection with FIGS. 1-4, i.e., the heatexchanger of a CRAC unit, the rear door heat exchanger, the heatexchanger of the coolant distribution unit, and the heat exchanger ofthe modular cooling unit.

FIGS. 6A & 6B illustrate graphical representations of pre-characterizedcorrelation data collected for a generic heat exchanger, such asdepicted in FIG. 5. FIG. 6A depicts correlation data for the conditionwhere fluid A flow rate has a lower heat capacity rate, and FIG. 6Billustrates the condition where the fluid B flow rate has a lower heatcapacity rate. The heat capacity rate is defined as the product of thefluid's volumetric flow rate, the fluid density, and the fluid specificheat. The density and specific heat are thermophysical quantities of thefluids, which are readily available in heat transfer handbooks or othersuch technical sources. In both FIGS. 6A & 6B, heat exchangereffectiveness is plotted on the y-axis versus fluid A flow rate on thex-axis, and several curves are generated for different values of fluid Bflow rate. The numeric quantities on the x-axis represent various flowsettings during laboratory testing for the fluid A loop (0 . . . X10, orY1 . . . Y6), and the flow rate setting flowB 2 is greater than the flowrate setting flowB 1, flowB 3 is greater than the flow rate settingflowB 2, etc. (again, by way of example only).

A significant thermal performance metric for any heat exchanger is itseffectiveness. Effectiveness in this instance is defined as the ratio ofthe actual heat transferred from one fluid stream to another, to thetheoretical maximum heat transfer possible for certain given inlet fluidtemperature values. Effectiveness is a measure of how well a given heatexchanger is designed, and how well the heat exchanger performs undercertain input conditions (e.g., flow rates). This is a characteristic ofthe heat exchanger, and is determined by its physical design, thethermophysical properties of the materials that are used in itsconstruction, the thermophysical properties of the fluids that flowthrough it, and the heat capacity rates of the fluids flowing throughthe device. In practical terms, effectiveness may be calculated usingthe ratio of two temperature difference terms. The numerator is theabsolute temperature change in the fluid stream which has the smaller ofthe two heat capacity rates, with the heat capacity rate beingcalculated as the product of the volumetric flow rate, the fluidspecific heat, and the density. The denominator is the temperaturedifference between the fluid at the inlet of the hot stream and thefluid at the inlet of the cold stream. The numerical value of thedenominator represents the maximum available temperature difference thatis driving the heat exchange. Thus, for the cases shown in FIG. 6A, theeffectiveness can be calculated using the ratio of (T_(A2)−T_(A1)) to(T_(B1)−T_(A1)), when fluid A is the cold stream fluid. For the casesshown in FIG. 6B, effectiveness is the ratio of (T_(B1)−T_(B2)) to(T_(B1)−T_(A1)), when fluid B is the hotter of the two fluid streams.Whether the fluid stream is hot or cold changes the equations of thenumerator and the denominator to maintain a positive sign (while usingthe same parameters).

The curves of FIGS. 6A & 6B have different shapes because the fluid Aflow rate impacts heat exchanger effectiveness differently in the twocases, i.e., when fluid A has the lower heat capacity rate (FIG. 6A),versus when fluid A has the higher heat capacity rate (FIG. 6B). Basedupon heat exchanger theory, it is known that the effectiveness of a heatexchanger is inversely dependent on the ratio of the fluid heat capacityrates (smaller over the larger). Thus, in FIG. 6A, as fluid A flow rateis increased for a fixed fluid B flow rate, the heat capacity rate ratiobecomes larger, and the effectiveness reduces. In FIG. 6B, as fluid Aflow rate increases, its heat capacity rate also increases, and theratio becomes smaller, thus resulting in a higher heat exchangereffectiveness. Both FIGS. 6A & 6B display three equations each (by wayof example only), which describe the relationship from the correlationdata allowing the estimation of fluid A flow rate when the effectivenessand fluid B flow rate are known. Knowledge of fluid B flow rate isneeded to know which set of constants to use, such as the constantsR_(i), S_(i) in the case of FIG. 6A, or P_(i), Q_(i) in the case of FIG.6B, which are functions of the fluid B flow rate. For example, in FIG.6A, for a fluid B flow rate of flowB 1, the corresponding constants areR₁ and S₁. Similarly, in FIG. 6B, if the fluid B flow rate is flowB 4,the corresponding constants are P₄ and Q₄.

The equations of the form shown in FIGS. 6A & 6B, derived via laboratorytesting, can be used in accordance with the invention described hereinto calculate the correct fluid A and fluid B flow rates when thetemperatures at the air inlets (T_(A1), T_(B1)) and outlets (T_(A2),T_(B2)) of the two fluid loops of the heat exchanger are known.

FIGS. 7A-7D are a graphical depiction of the steps followed to convergeon a correct flow rate for fluid A and fluid B, when fluid heat capacityrate of fluid A is lower than that of fluid B. The actual value ofeffectiveness is a known, determined quantity, as is the correct valuefor the ratio of the smaller to the larger fluid heat capacity rates(i.e., the heat capacity rate ratio (C)). In the case of FIGS. 7A-7D,this ratio is equal to the fluid A heat capacity rate divided by thefluid B heat capacity rate. How these quantities are calculated isdescribed in greater detail below with reference to the flowchart ofFIGS. 9-13.

In a first step, illustrated in FIG. 7A, an initial estimate of flowB 1is made for fluid B flow rate, and the associated constants R₁ and S₁are obtained, for example, via a lookup table using thepre-characterized correlation data illustrated in FIG. 6A. Using theseconstants and the known value of effectiveness, the corresponding flowrate of fluid A is calculated. Using the estimated value of fluid B flowrate, and the calculated value of fluid A flow rate, the two fluid heatcapacity rates are computed, and then the estimated heat capacity rateratio (C_(est)) is calculated. In FIGS. 7A-7D, the upper lines are forthe higher fluid B flow rates (i.e., flowB 1>flowB 2>flowB 3), andtherefore, the initial estimate of flowB 1 results in a low value of thecalculated heat capacity rate ratio (C_(est)). In FIG. 7B, a second stepis illustrated, wherein a second estimate of fluid B flow rate, flowB 2,also results in a low value of the estimated heat capacity rate ratio(C_(est)) when compared to the true, measured heat capacity rate ratio(C). In FIG. 7C, a further step is illustrated, wherein a new estimateof fluid B flow rate of flowB 3 results in a high value for thecalculated heat capacity rate ratio (C_(est)). Thus, two bounding valuesof fluid B flow rate are identified. In FIG. 7D, a further step ofinterpolation leads the process to a correct value of fluid B flow rate,as well as the correct values of the R and S constants, and thus thecorrect value for fluid A flow rate. The identification of the correctflow rates results in the calculated heat capacity rate ratio (C_(est))being exactly equal to the determined actual capacity ratio (C) for theheat exchanger.

FIGS. 8A-8D are a graphical depiction of the various steps required toconverge on a correct flow rate for fluid A and fluid B when fluid Bheat capacity rate is lower than that of fluid A. The actual value ofeffectiveness is again a known, determined quantity (as explainedbelow), as is the correct value for the ratio of the smaller to thelarger fluid heat capacity rates. In the case of FIGS. 8A-8D, this ratiois equal to the fluid B heat capacity rate divided by the fluid A heatcapacity rate. How these quantities are calculated is described ingreater detail below with reference to FIGS. 9-13.

In a first step illustrated in FIG. 8A, an initial estimate of flowB 4is made for the fluid B flow rate, and the associated constants P₄ andQ₄ are identified, for example, via a lookup table, from thepre-characterized correlation data of FIG. 6B. Using these constants,and the determined value of the effectiveness, the fluid A flow rate iscalculated. Using the estimated fluid B flow rate and the calculatedfluid A flow rate, the two fluid heat capacity rates are computed, andthen the estimated heat capacity rate ratio (C_(est)) is determined. InFIGS. 8A-8D, the upper lines are for the lower fluid B flow rates, i.e.,flowB 4<flowB 5<flowB 6, etc. Therefore, the initial estimate results ina low value of the calculated heat capacity rate ratio (C_(est)).

In FIG. 8B, a second step is illustrated, wherein a second estimate forfluid B flow rate (i.e., flowB 5), also results in a low value of theheat capacity rate ratio (C_(est)) when compared to the true capacityratio (C). In FIG. 8C, a third step is illustrated, where a new estimateof fluid B flow rate, flowB 6, results in a high value for thecalculated heat capacity rate ratio (C_(est)). Thus, the two boundingvalues of fluid B flow rate are identified. In FIG. 8D, a further stepof interpolation leads the process to the correct value of fluid B flowrate, the correct values of the P and Q constants, and thus, the correctvalue for fluid A flow rate. The identification of the correct flowrates, again results in the calculated heat capacity rate ratio(C_(est)) being equal to the actual determined capacity ratio (C).

FIGS. 9-13 illustrate one embodiment of a heat exchanger monitoringprocess, in accordance with an aspect of the present invention. Theflowchart of these figures comprises processing embedded within themonitor unit which allows temperature sensor data to be converted toheat exchanger fluid flow rates, and subsequently output, for example,by display, at the monitor unit. A site engineer can then periodicallyemploy the outputted fluid flow rates to verify proper functioning ofthe heat exchanger or fluid distribution network supplying the heatexchanger. Additionally, the determined fluid flow rates through theheat exchanger can be employed to determine the heat exchange ratebetween a fluid A loop and fluid B loop of the heat exchanger. Thisinformation can be employed, for example, to monitor heat dissipationrate of a particular electronics rack within the data center. Theinformation can also be employed in evaluating total load on the one ormore air-conditioning units of a data center to determine how close tototal cooling capacity the data center is being operated. Thisinformation can be useful for future planning purposes.

FIG. 9 illustrates an initial phase of the heat exchanger monitoringprocess 900. As a first step, the monitor or control unit obtains datafrom the various temperature sensors 901. Specifically, the fluid Ainlet temperature T_(A1), fluid A outlet temperature T_(A2), fluid Binlet temperature T_(B1), and fluid B outlet temperature T_(B2) areobtained. In a next step, a check is made to determine whether fluid Aor fluid B is the hot stream, that is, whether T_(A1) is greater thanT_(B1) 902. If “yes”, then the control unit determines a first set ofderived parameters 904. This first set of derived parameters includesΔT_(inlet), ΔT_(A), and ΔT_(B). These parameters, which are defined inTable 1 below, are also determined by the control unit if T_(A1) is notgreater than T_(B1), only the difference quantities are calculated withthe sequence in parameters switched to ensure a positive sign for thetemperature differences 906. In a next step, the temperature differencebetween T_(A1) and T_(A2) is compared to that between T_(B1) and T_(B2)908. Since the heat lost or gained by one fluid is equal to the heatloss or gain of the other fluid, this comparison yields knowledgeregarding which fluid loop (A or B) has the lower heat capacity rate.The fluid loop with the lower heat capacity rate experiences a largertemperature difference across its inlet and outlet. If the comparisoncarried out in step 908 yields a positive result, then fluid A has alower heat capacity rate 910 and processing proceeds to FIG. 10.Otherwise, if the comparison carried out in step 908 yields a negativeresult, then fluid B has a lower heat capacity rate than fluid A 912,and processing proceeds to FIG. 12.

Continuing first with FIG. 10, the control unit initially determines asecond set of derived parameters 920. This second set of parametersincludes the effectiveness (ε) and the true or actual heat capacity rateratio (C) of the heat exchanger. The heat exchanger heat capacity rateratio is the ratio of the smaller fluid heat capacity rate to the largerfluid heat capacity rate. In the case of FIG. 10, fluid A has the lowerheat capacity rate (as determined above in connection with FIG. 9).Processing then identifies bounding values for the fluid B flow rateusing the correlated data 922. This identification of bounding valuesincludes several sub-steps, as illustrated in FIG. 10 and describedbelow.

In a first sub-step, the fluid B flow rate is set to an estimatedflowB_(i) value, which is a pre-characterized fluid B flow rate, forexample, flowB, may be the largest fluid B flow rate tested in thepre-characterizing laboratory testing of the heat exchanger 924. Thisvalue of fluid B flow rate is chosen to be much larger than thespecified fluid B flow rate and is a reasonable estimate of the largestfluid B flow rate that the heat exchanger would be expected toexperience in the field. Via a lookup table, the pre-characterizedcorrelation data is employed to obtain constants R_(i) and S_(i), whichare associated with the equation relating fluid A flow rate to heatexchanger effectiveness for the fluid B flow rate of flowB_(i). Usingthe effectiveness calculated above in step 920, and the identifiedconstants R_(i) and S_(i), the fluid A flow rate, flowA_(i) isdetermined 926. In the next sub-step, the two estimated values for thefluid heat capacity rates (for fluid A and fluid B) are determined, andthese values are used to estimate a value for the heat capacity rateratio (C_(est, i)) 928. Since the process began with a high estimatedvalue for fluid B flow rate, and fluid B heat capacity rate is thedenominator of the equation for the heat capacity rate ratio (for fluidB), this initial estimated value for heat capacity rate ratio (C_(est))is likely to be smaller than the actual heat capacity rate ratio (C). Inthe next sub-step, the comparison is made between the estimated and theactual heat capacity rate ratios 930. A positive result leads to counteri being incremented by 1 932, and processing returning to step 924,which results in the fluid B flow rate being incremented in a sequentialmanner through the pre-characterized correlation data. This processcontinues until a fluid B flow rate is identified for which theestimated heat capacity rate ratio (C_(est)) is larger than the actualheat capacity rate ratio (C). If the result occurs for a count i, thenthe fluid B flow rates, fluid B_(i-1), and fluid B_(i) are the boundingvalues for the correct fluid B flow rate. A negative result in sub-step930 leads processing to check whether the value of the counter isgreater than 1 934. If “no”, then the first estimated value of fluid Bflow rate is actually lower than the real fluid B flow rate. This inturn means that the heat exchanger is running out of specification (onthe high side) with respect to the fluid B flow rate, and acorresponding warning 936 is issued, before processing returns to FIG.9. If i is other than 1, then the two bounding flow rates for the fluidB flow rate have been identified, and processing proceeds to FIG. 11.

As shown in FIG. 11, the control unit initially determines a third setof derived parameters 940. These derived parameters include thedifference between the heat capacity rate ratio for the upper bound offluid B flow rate (C_(est, i-1)) and the heat capacity rate ratio forthe lower bound of fluid B (C_(est, i)). The difference between the heatcapacity rate ratio for the upper bound of fluid B (C_(est, i-1)) andthe actual heat capacity rate ratio (C) is also determined. The ratio ofthese two differences represents the fractional “distance” to thelocation of the actual values (flowB, R & S) that needs to be traversedfrom the i-1 lower bound values. In subsequent sub-steps, the actualvalues of flowB, R & S are determined using this fractional difference.Then, using the correct values for R and S, and the knowledge of theactual effectiveness, the actual fluid A flow rate is determined. Ifdesired, the heat transfer rate across the heat exchanger can also bedetermined as the product of flowA, the density of fluid A, the specificheat of fluid A and the inlet-to-outlet fluid A temperature differencedetermined via the processing of FIG. 9.

In a next step, which includes four sub-steps that may be executed inparallel, the fluid A and fluid B flow rates are compared to respectiveupper and lower bound specifications for each fluid loop, and adetermination is made whether the flow rates are in specification or outof specification. If any of the flow rates are out of specification,then an appropriate warning message is automatically generated foroutput.

Specifically, processing determines whether flowA is less than aspecified low fluid A flow rate 942, and if so, an appropriate fluid Aflow rate out of specification-low warning is issued 944. Processingalso determines whether flowA is greater than the specified high flowrate for fluid A 946, and if so, issues a warning that fluid A flow rateis out of specification (on the high side) 948. If flowB is less thanthe specified low fluid B flow rate 950, then a warning is issued thatthe fluid B flow rate is out of specification 952 (on the low side), andif flow B is greater than the specified high fluid B flow rate 954, thena warning is issued that the fluid B flow rate is out of specification(on the high side) 956. The heat transfer rate, two fluid flow rates,and any warning messages are next output, for example, displayed 958. Asused herein, “output” refers to displaying, saving, printing orotherwise providing the determined results to or for use of, forexample, a central administrator of the data center within which theheat exchanger being monitored resides. Processing then waits a definedtime interval t₁ 960 before returning to automatically obtain a new setof temperature sensor readings 901 (FIG. 9), and repeating thedetermination of fluid A and fluid B flow rates.

As noted above, FIGS. 10 & 11 describe processing employed when fluid Ais determined to have a lower heat capacity rate than fluid B. FIGS. 12& 13 provide the analogous processing in the event that fluid B has alower heat capacity rate than fluid A.

As illustrated, FIG. 12 begins with the control unit determining asecond set of derived parameters 962, including the heat exchangereffectiveness (ε), and the heat exchanger heat capacity rate ratio (C).The heat exchanger heat capacity rate ratio is the ratio of the smallerfluid heat capacity rate to the larger fluid heat capacity rate. In thisexample, fluid B has the lower heat capacity rate, and fluid A thehigher heat capacity rate. Next, the control unit employs a subroutineto determine estimated fluid B and fluid A flow rates and an estimatedheat capacity rate ratio (C_(est)) for the heat exchanger 964.Specifically, the fluid B flow rate is set to flowB_(j), which is apredetermined, smallest fluid B flow rate tested in the laboratorytesting of the heat exchanger 966. This value of fluid B flow rate istypically lower than the specified low value and is a reasonableestimate of the lowest fluid B flow rate that the heat exchanger mightexperience in the field. Via a lookup table, the constants P_(j) andQ_(j) associated with the equation relating fluid A flow rate to theheat exchanger effectiveness (for the fluid B flow rate equal toflowB_(j)) are identified, and using the effectiveness determined above,and the identified constants P_(j) & Q_(j), the estimated fluid A flowrate, (flowA_(j)) is determined 968.

In a next step, the two estimated values for fluid heat capacity rates(fluid A and fluid B) are determined, and using these values, anestimated value for the heat capacity rate ratio (C_(est)) is determined970. Since processing began with a low estimated value for fluid B flowrate, and the fluid heat capacity rate is in the numerator of theequation for heat capacity rate ratio, this initial estimated value ofheat capacity rate ratio may be smaller than the actual ratio. In a nextstep 972, a comparison is thus made between the heat capacity rateratios. If the actual heat capacity rate ratio (C) is larger than theestimated heat capacity rate ratio (C_(est)), then index j isincremented by 1 974, and the subroutine repeats. Thus, fluid B flowrate is incremented in a sequential manner, until a fluid B flow rate isidentified for which the estimated heat capacity rate ratio (C_(est)) islarger than the actual heat capacity rate ratio (C). If this resultoccurs for counter index j, then the fluid B flow rates, flowB_(j-1) andflowB_(j) are the bounding values for the correct fluid B flow rate. Anegative result in the comparison of step 972, leads to processingchecking whether j is equal to 1 976. If j equals 1, then the firstestimated value of fluid B flow rate is actually higher than the realfluid B flow rate. This in turn means that the heat exchanger is runningbelow specification with respect to the fluid B flow rate, and a warningis issued that fluid B flow rate is out of specification (on the lowside) 978, after which processing returns to FIG. 9. If the estimatedheat capacity rate ratio is greater than the actual heat capacity rateratio, and j is greater than 1, then the two bounding flow rates forfluid B flow rate have been identified, and processing proceeds to FIG.13.

Referring to FIG. 13, processing initially determines a differencebetween the heat capacity rate ratio for the upper bound of the fluid Bflow rate (C_(est, j)) and the heat capacity rate ratio for the lowerbound of the fluid B flow rate (C_(est i-1)) 980. Next, the differencebetween the actual heat capacity rate ratio (C) and the heat capacityrate ratio for the lower bound of fluid B (C_(est, j-1)) is determined.The ratio of these two differences represents the fractional “distance”to the location of the actual values for flowB, P & Q that need to betraveled from the lower (j-1) bound values. In subsequent steps, theactual values of flowB, P & Q are calculated using this fractionaldistance. Then, using the actual values for P & Q, and the knowledge ofthe actual effectiveness, the actual fluid A flow rate is determined.The heat transfer rate (Power_(Hx)) across the heat exchanger can alsobe determined as the product of the flowB, the density of fluid B, thespecific heat of fluid B, and the inlet-to-outlet fluid B temperaturedifference determined above via the processing of FIG. 9.

In a next step, which includes four sub-steps that may be executed inparallel, the fluid A and fluid B flow rates are compared to upper andlower bound specifications for each fluid loop, and a determination ismade whether the flow rates are in specification or out ofspecification. If any of the fluid flow rates are out of specification,then an appropriate warning message is generated. Specifically,processing determines whether fluid flowA is less than a specified lowflow rate 982, and if so, generates a warning that fluid A flow rate isout of specification (on the low side) 984. In addition, processingdetermines whether flowA is greater than a specified high flow rate 986,and if “yes”, generates a warning that fluid A flow rate is out ofspecification (on the high side) 988. Processing also determines whetherfluid B flow rate is less than a specified low flow rate 990, and if“yes”, generates a warning that fluid B flow rate is out ofspecification (on the low side) 992. Further, processing determineswhether flowB is greater than a specified high flow rate 994, and if“yes”, generates a warning that fluid B flow rate is out ofspecification (on the high side) 996.

The heat transfer rate (Power_(Hx)), two fluid flow rates (flowA, flowB)and any warning message are the output 998, for example, to a datacenter administrator or site engineer for possible adjustment of one ormore of the flow rates, or to take action based upon one or morewarnings generated. Processing then waits a defined time interval t₁1000, before automatically returning to obtain a new set of temperaturereadings 901 (FIG. 9) and repeating the determination of fluid A andfluid B flow rates.

TABLE 1 Variable/Equation Definition T_(A1) Fluid temperature measuredvia sensor located at inlet to loop A, ° C. T_(A2) Fluid temperaturemeasure via sensor located at outlet to loop A, ° C. T_(B1) Fluidtemperature measured via sensor located at inlet to loop B, ° C. T_(B2)Fluid temperature measured via sensor located at outlet to loop B, ° C.ΔT_(A) Absolute difference between inlet and outlet fluid temperaturesof loop A, ° C. ΔT_(B) Absolute difference between inlet and outletfluid temperatures of loop B, ° C. ΔT_(inlet) Absolute difference intemperature between the inlets of loop A and B, ° C. flowA Volumetricfluid flow rate in loop A, m³/s. flowB Volumetric fluid flow rate inloop B, m³/s. R, S, P, Q Constants used to fit functions to lab datarelating effectiveness and the fluid flow rate through loop A of theheat exchanger. Values for these constants depend on value of the fluidB flow rate. C True value for the ratio of the minimum fluid heatcapacity rate to the maximum fluid heat capacity rate. C_(est) Estimatedvalue for the ratio of the minimum fluid heat capacity rate to themaximum fluid heat capacity rate. ΔC_(est) Bounding distance for thevalue of the C between (i-1)^(th) and i^(th) iteration. ΔC* Truedistance for the true value of C from (i-1)^(th) iteration. ΔR, ΔS, ΔP,ΔQ Bounding distance for true values of constants R, S, P and Q,respectively, between (i-1)^(th) and i^(th) iteration. ΔflowB Boundingdistance for the true value of volumetric flow rate in loop B, between(i-1)^(th) and i^(th) iteration, m³/s. C_(A, est) Estimated heatcapacity rate of the fluid in loop A, W/K. C_(B, est) Estimated heatcapacity rate of the fluid in loop B, W/K. ε True value for the heatexchanger effectiveness. It represents the ratio of the actual heatexchanged between the fluid streams versus the maximum possible heatthat could be exchanged. This is a characteristic of the heat exchangerand is determined by its physical design, the thermophysical propertiesof the materials that are used in its construction, the thermophysicalproperties of the fluids that flow through it, and the mass flow ratesof the fluids that flow through the device. Power_(Hx) Heat exchangerate between the loop A and loop B of the heat exchanger, W. ρA Massdensity of fluid in loop A, kg/m³. C_(ρA) Specific heat of fluid in loopA, J/kg-K. ρB Mass density of fluid in loop B, kg/m³. C_(ρB) Specificheat of fluid in loop B, J/kg-K. i Counter in logic loops. low spec ALowest allowable value of volumetric flow rate in loop A, m³/s. highspec A Highest allowable value of volumetric flow rate in loop A, m³/s.low spec B Lowest allowable value of volumetric flow rate in loop B,m³/s. high spec B Highest allowable value of volumetric flow rate inloop B, m³/s. t₁ Time delay after the logic is executed and a newexecution is started, s.

More particularly, the heat exchanged between the two fluid streams viathe heat exchange device is given by:q=ε×C _(min) ×ΔT _(inlet)  (1)

Where ε is the heat exchanger effectiveness, and ΔT_(inlet) is the inlettemperature difference that is driving the heat exchange between the twofluid streams that are flowing in the heat exchanger. Also, in equation(1) above, the parameter C_(min) is the minimum of the two fluid streamheat capacity rates. If the heat capacity rate of the fluid in loop A isthe lower of the two, then equation (1) becomes:q=ε×C _(A) ×ΔT _(inlet)  (2)

The heat transferred to the fluid in loop A will change the fluidtemperature, between the inlet and the outlet, and can be calculatedusing:q=C _(A) ×ΔT _(A)  (3)

Combining equations (2) and (3) to solve for ε, yields,ε=ΔT _(A) /ΔT _(inlet)  (4)

If the fluid loop B has the lower of the two heat capacity rates, thenequation (4) becomes:ε=ΔT _(B) /ΔT _(inlet)  (5)

This fluid loop A flow rate can be expressed as a function of theeffectiveness and is a function of the fluid loop B flow rate and can becalibrated in the lab to yield the following functions:flowA=[Ln(R)−Ln(ε)]/S if flowB>flowA  (6)flowA=ε ^([(ε+P)/Q]) if flowA>flowB  (7)

Where R, S, P and Q are constants which depend on the value of flow B.

Once the fluid flow rates are known, then the heat exchanged between thetwo loops of the heat exchanger can be calculated using:Power_(Hx) =C _(A) ×ΔT _(A) =C _(B) ×ΔT _(B)  (8)

The detailed description presented above is discussed in terms ofprocedures which can be executed on a computer, a network or a clusterof computers. These procedural descriptions and representations are usedby those skilled in the art to most effectively convey the substance oftheir work to others skilled in the art. They may be implemented inhardware or software, or a combination of the two.

A procedure is here, and generally, conceived to be a sequence of stepsleading to a desired result. These steps are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, transferred, combined, compared, and otherwisemanipulated. It proves convenient at times, principally for reasons ofcommon usage, to refer to these signals as bits, values, elements,symbols, characters, terms, numbers, objects, attributes or the like. Itshould be noted, however, that all of these and similar terms are to beassociated with the appropriate physical quantities and are merelyconvenient labels applied to these quantities.

Further, the manipulations performed are often referred to in terms,such as closing or opening, which are commonly associated with manualoperations performed by a human operator. No such intervention of ahuman operator is necessary in the operations described herein whichform part of the present invention; the operations may be implemented asautomatic machine operations. Useful machines for performing theoperations of the present invention include general purpose digitalcomputers or similar devices.

Aspects of the invention are preferably implemented in a high levelprocedural or object-oriented programming language to communicate with acomputer. However, the inventive aspects can be implemented in assemblyor machine language, if desired. In any case, the language may be acompiled or interpreted language.

The invention may be implemented as a mechanism or a computer programproduct comprising a recording medium. Such a mechanism or computerprogram product may include, but is not limited to CD-ROMs, diskettes,tapes, hard drives, computer RAM or ROM and/or the electronic, magnetic,optical, biological or other similar embodiment of the program. Indeed,the mechanism or computer program product may include any solid or fluidtransmission medium, magnetic or optical, or the like, for storing ortransmitting signals readable by a machine for controlling the operationof a general or special purpose programmable computer according to themethod of the invention and/or to structure its components in accordancewith a system of the invention.

Aspects of the invention may be implemented in a system. A system maycomprise a computer that includes a processor and a memory device andoptionally, a storage device, an output device such as a video displayand/or an input device such as a keyboard or computer mouse. Moreover, asystem may comprise an interconnected network of computers. Computersmay equally be in stand-alone form (such as the traditional desktoppersonal computer) or integrated into another environment (such as apartially clustered computing environment). The system may be speciallyconstructed for the required purposes to perform, for example, themethod steps of the invention or it may comprise one or more generalpurpose computers as selectively activated or reconfigured by a computerprogram in accordance with the teachings herein stored in thecomputer(s). The procedures presented herein are not inherently relatedto a particular computing environment. The required structure for avariety of these systems will appear from the description given.

The capabilities of one or more aspects of the present invention can beimplemented in software, firmware, hardware or some combination thereof.

One or more aspects of the present invention can be included in anarticle of manufacture (e.g., one or more computer program products)having, for instance, computer usable media. The media has therein, forinstance, computer readable program code means or logic (e.g.,instructions, code, commands, etc.) to provide and facilitate thecapabilities of the present invention. The article of manufacture can beincluded as a part of a computer system or sold separately.

Additionally, at least one program storage device readable by a machineembodying at least one program of instructions executable by the machineto perform the capabilities of the present invention can be provided.

The flow diagrams depicted herein are just examples. There may be manyvariations to these diagrams or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order, or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the following claims.

1. A method of monitoring a heat exchanger, the method comprising:pre-characterizing the heat exchanger to generate pre-characterizedcorrelation data for the heat exchanger, the pre-characterizedcorrelation data comprising data correlating effectiveness of the heatexchanger to flow rates of a first fluid through the heat exchanger andflow rates of a second fluid through the heat exchanger, wherein whenoperational, heat is transferred across the heat exchanger between thefirst fluid and the second fluid; sensing, when operational, inlet andoutlet temperatures of the first fluid passing through the heatexchanger, and inlet and outlet temperatures of the second fluid passingthrough the heat exchanger; automatically determining at least one offlow rate of the first fluid through the heat exchanger or flow rate ofthe second fluid through the heat exchanger, the automaticallydetermining employing the pre-characterized correlation data and thesensed inlet and outlet temperatures of the first fluid and the sensedinlet and outlet temperatures of the second fluid; and outputting thedetermined flow rate of the first fluid or the flow rate of the secondfluid through the heat exchanger.
 2. The method of claim 1, wherein theautomatically determining comprises determining flow rate of the firstfluid through the heat exchanger and flow rate of the second fluidthrough the heat exchanger employing only the pre-characterizedcorrelation data and the sensed inlet and outlet temperatures of thefirst fluid and the sensed inlet and outlet temperatures of the secondfluid.
 3. The method of claim 2, wherein the pre-characterizingcomprises relating known flow rates of the first fluid through the heatexchanger and known flow rates of the second fluid through the heatexchanger to effectiveness of the heat exchanger, and wherein thepre-characterizing further comprises generating one or more equationsrelating flow rate of at least one of the first fluid or the secondfluid to effectiveness of the heat exchanger.
 4. The method of claim 1,wherein the automatically determining comprises employing the sensedinlet and outlet temperatures of the first fluid and the sensed inletand outlet temperatures of the second fluid in obtaining effectivenessof the heat exchanger and a heat capacity rate ratio for the heatexchanger, and wherein the method further comprises employing theeffectiveness and the heat capacity rate ratio in comparison with thepre-characterized correlation data in determining flow rate of the firstfluid and flow rate of the second fluid through the heat exchanger. 5.The method of claim 4, further comprising employing the sensed inlet andoutlet temperatures of the first fluid and the sensed inlet and outlettemperatures of the second fluid in determining whether the first fluidor the second fluid has a lower heat capacity rate, and wherein theautomatically determining comprises employing a first set ofpre-characterized correlation data if the first fluid has a lower heatcapacity rate than the second fluid, or employing a second set ofpre-characterized correlation data if the second fluid has a lower heatcapacity rate than the first fluid.
 6. The method of claim 5, whereinthe automatically determining comprises: identifying bounding values forat least one of the first fluid flow rate or the second fluid flow rateusing the pre-characterized correlation data, and wherein the usingcomprises: estimating the second fluid flow rate to be one flow rate ofthe second fluid in the pre-characterized correlation data; estimatingthe first fluid flow rate using the effectiveness, and constants derivedfrom the pre-characterized correlation data for the estimated secondfluid flow rate; determining an estimated heat capacity rate ratio forthe heat exchanger employing the estimated first fluid flow rate and theestimated second fluid flow rate; and wherein the identifying furthercomprises comparing the estimated heat capacity rate ratio for the heatexchanger to the determined heat capacity rate ratio for the heatexchanger, and if the estimated heat capacity rate ratio for the heatexchanger is less than the determined heat capacity rate ratio for theheat exchanger, repeating the using for a second fluid flow ratecomprising a next flow rate of the second fluid in the pre-characterizedcorrelation data, otherwise, identifying the currently estimated secondfluid flow rate and the just prior estimated second fluid flow rate asbounding second fluid flow rates from the pre-characterized correlationdata and employing the bounding second fluid flow rates in interpolatinga fluid flow rate for the second fluid, and interpolating values forconstants employed in relating the first fluid flow rate to heatexchanger effectiveness, and thereafter, determining the first fluidflow rate using the determined effectiveness and the interpolatedconstants.
 7. The method of claim 6, further comprising determining heattransfer rate across the heat exchanger employing one of the determinedfirst fluid flow rate or second fluid flow rate and outputting the heattransfer rate with the at least one of first fluid flow rate or thesecond fluid flow rate.
 8. The method of claim 1, further comprisingautomatically determining whether the first fluid flow rate is below afirst low specified flow rate, and if so, automatically issuing awarning that the first fluid flow rate is below the first low specifiedflow rate, automatically determining whether the first fluid flow rateis above a first high specified flow rate, and if so, automaticallyissuing a warning that the first fluid flow rate is above the first highspecified flow rate, automatically determining whether the second fluidflow rate is below a second low specified flow rate, and if so,automatically issuing a warning that the second fluid flow rate is belowthe second low specified flow rate, or automatically determining whetherthe second fluid flow rate is above a second high specified flow rate,and if so, automatically issuing a warning that the second fluid flowrate is above the second high specified flow rate.
 9. The method ofclaim 1, wherein the heat exchanger comprises a heat exchangerconfigured to facilitate cooling of one or more electronic componentswithin a data center.
 10. A monitoring system for a heat exchanger, themonitoring system comprising: a database holding pre-characterizedcorrelation data for the heat exchanger, the pre-characterizedcorrelation data comprising data correlating effectiveness of the heatexchanger to flow rates of a first fluid through the heat exchanger andflow rates of a second fluid through the heat exchanger, wherein whenoperational, heat is transferred across the heat exchanger between thefirst fluid and the second fluid; a first inlet temperature sensor forsensing inlet temperature of the first fluid passing through the heatexchanger, when operational, and a first outlet temperature sensor forsensing outlet temperature of the first fluid passing through the heatexchanger; a second inlet temperature sensor for sensing inlettemperature of the second fluid passing through the heat exchanger, whenoperational, and a second outlet temperature sensor for sensing outlettemperature of the second fluid passing through the heat exchanger; anda monitor unit coupled to the first and second inlet temperature sensorsand the first and second outlet temperature sensors for obtaining thesensed inlet and outlet temperatures of the first fluid and the secondfluid and for employing the sensed inlet and outlet temperatures of thefirst fluid and the second fluid and the pre-characterized correlationdata in automatically determining at least one of flow rate of the firstfluid through the heat exchanger or flow rate of the second fluidthrough the heat exchanger, and outputting the determined flow rate ofthe first fluid or the flow rate of the second fluid through the heatexchanger.
 11. The monitoring system of claim 10, wherein the monitorunit determines flow rate of the first fluid through the heat exchangerand flow rate of the second fluid through the heat exchanger employingonly the pre-characterized correlation data and the sensed inlet andoutlet temperatures of the first fluid and the sensed inlet and outlettemperatures of the second fluid.
 12. The monitoring system of claim 10,wherein the monitor unit employs the sensed inlet and outlettemperatures of the first fluid and the sensed inlet and outlettemperatures of the second fluid in obtaining effectiveness of the heatexchanger and a heat capacity rate ratio for the heat exchanger, andwherein the method further comprises employing the effectiveness and theheat capacity rate ratio in comparison with the pre-characterizedcorrelation data in determining flow rate of the first fluid and flowrate of the second fluid through the heat exchanger.
 13. The monitoringsystem of claim 12, wherein the monitor unit employs the sensed inletand outlet temperatures of the first fluid and the sensed inlet andoutlet temperatures of the second fluid in determining whether the firstfluid or the second fluid has a lower heat capacity rate, and whereinthe automatically determining comprises employing a first set ofpre-characterized correlation data if the first fluid has a lower heatcapacity rate than the second fluid, or employing a second set ofpre-characterized correlation data if the second fluid has a lower heatcapacity rate than the first fluid.
 14. The monitoring system of claim13, wherein the monitor unit: identifies bounding values for at leastone of the first fluid flow rate or the second fluid flow rate using thepre-characterized correlation data, and wherein the using comprises:estimating the second fluid flow rate to be one flow rate of the secondfluid in the pre-characterized correlation data; estimating the firstfluid flow rate using the effectiveness, and constants derived from thepre-characterized correlation data for the estimated second fluid flowrate; determining an estimated heat capacity rate ratio for the heatexchanger employing the estimated first fluid flow rate and theestimated second fluid flow rate; and comparing the estimated heatcapacity rate ratio for the heat exchanger to the determined heatcapacity rate ratio for the heat exchanger, and if the estimated heatcapacity rate ratio for the heat exchanger is less than the determinedheat capacity rate ratio for the heat exchanger, repeats the using for asecond fluid flow rate comprising a next flow rate of the second fluidin the pre-characterized correlation data, otherwise, identifies thecurrently estimated second fluid flow rate and the just prior estimatedsecond fluid flow rate as bounding second fluid flow rates from thepre-characterized correlation data and employs the bounding second fluidflow rates in interpolating a fluid flow rate for the second fluid, andinterpolates values for constants employed in relating the first fluidflow rate to heat exchanger effectiveness, and thereafter, determinesthe first fluid flow rate using the determined effectiveness and theinterpolated constants.
 15. The monitoring system of claim 14, whereinthe monitor unit further determines a heat transfer rate across the heatexchanger employing one of the determined first fluid flow rate orsecond fluid flow rate and outputs the heat transfer rate with the atleast one of first fluid flow rate or the second fluid flow rate. 16.The monitoring system of claim 10, wherein the monitor unitautomatically determines whether the first fluid flow rate is below afirst low specified flow rate, and if so, automatically issues a warningthat the first fluid flow rate is below the first low specified flowrate, automatically determines whether the first fluid flow rate isabove a first high specified flow rate, and if so, automatically issuesa warning that the first fluid flow rate is above the first highspecified flow rate, automatically determines whether the second fluidflow rate is below a second low specified flow rate, and if so,automatically issues a warning that the second fluid flow rate is belowthe second low specified flow rate, or automatically determines whetherthe second fluid flow rate is above a second high specified flow rate,and if so, automatically issues a warning that the second fluid flowrate is above the second high specified flow rate.
 17. A data centercomprising: a heat exchanger for facilitating cooling of at least oneelectronics rack within the data center; and a monitoring system for theheat exchanger, the monitoring system comprising: a database holdingpre-characterized correlation data for the heat exchanger, thepre-characterized correlation data comprising data correlatingeffectiveness of the heat exchanger to flow rates of a first fluidthrough the heat exchanger and flow rates of a second fluid through theheat exchanger, wherein when operational, heat is transferred across theheat exchanger between the first fluid and the second fluid; a firstinlet temperature sensor for sensing inlet temperature of the firstfluid passing through the heat exchanger, when operational, and a firstoutlet temperature sensor for sensing outlet temperature of the firstfluid passing through the heat exchanger; a second inlet temperaturesensor for sensing inlet temperature of the second fluid passing throughthe heat exchanger, when operational, and a second outlet temperaturesensor for sensing outlet temperature of the second fluid passingthrough the heat exchanger; and a monitor unit coupled to the first andsecond inlet temperature sensors and the first and second outlettemperature sensors for obtaining the sensed inlet and outlettemperatures of the first fluid and the second fluid, and for employingthe sensed inlet and outlet temperatures of the first fluid and thesecond fluid and the pre-characterized correlation data in automaticallydetermining at least one of flow rate of the first fluid through theheat exchanger or flow rate of the second fluid through the heatexchanger, and outputting the determined flow rate of the first fluid orthe flow rate of the second fluid through the heat exchanger.
 18. Thedata center of claim 17, wherein the monitor unit employs the sensedinlet and outlet temperatures of the first fluid and the sensed inletand outlet temperatures of the second fluid in obtaining effectivenessof the heat exchanger and a heat capacity rate ratio for the heatexchanger, and employs the effectiveness and the heat capacity rateratio in comparison with the pre-characterized correlation data indetermining flow rate of the first fluid and flow rate of the secondfluid through the heat exchanger.
 19. The data center of claim 18,wherein the monitor unit employs the sensed inlet and outlettemperatures of the first fluid and the sensed inlet and outlettemperatures of the second fluid in determining whether the first fluidor the second fluid has a lower heat capacity rate, and wherein theautomatically determining employs a first set of pre-characterizedcorrelation data if the first fluid has a lower heat capacity rate thanthe second fluid, or employs a second set of pre-characterizedcorrelation data if the second fluid has a lower heat capacity rate thanthe first fluid.
 20. The data center of claim 19, wherein the monitorunit: identifies bounding values for at least one of the first fluidflow rate or the second fluid flow rate using the pre-characterizedcorrelation data, and wherein the using comprises: estimating the secondfluid flow rate to be one flow rate of the second fluid in thepre-characterized correlation data; estimating the first fluid flow rateusing the effectiveness, and constants derived from thepre-characterized correlation data for the estimated second fluid flowrate; determining an estimated heat capacity rate ratio for the heatexchanger employing the estimated first fluid flow rate and theestimated second fluid flow rate; and comparing the estimated heatcapacity rate ratio for the heat exchanger to the determined heatcapacity rate ratio for the heat exchanger, and if the estimated heatcapacity rate ratio for the heat exchanger is less than the determinedheat capacity rate ratio for the heat exchanger, repeats the using for asecond fluid flow rate comprising a next flow rate of the second fluidin the pre-characterized correlation data, otherwise, identifies thecurrently estimated second fluid flow rate and the just prior estimatedsecond fluid flow rate as bounding second fluid flow rates from thepre-characterized correlation data and employs the bounding second fluidflow rates in interpolating a fluid flow rate for the second fluid, andinterpolates values for constants employed in relating the first fluidflow rate to heat exchanger effectiveness, and thereafter, determinesthe first fluid flow rate using the determined effectiveness and theinterpolated constants.